Stop motion



A. EDELMAN ET AL STOP MOTION 2 Sheets-Sheet 1 INVENTO m w L m m E WW N Eo v .R R U 0 Ma i T MT T n f A ,Am

June 21, 1955 Filed June 25, 1949 June 21, 1955 A. EDELMAN ET AL2,711,093

STOP MOTIYON Filed June 25, 1.949

2 Sheets-Sheet 2 INVENTORLS. ABRAHAM EDELMAN.

ROBERT H- ROUGHSEDGE y HANS G. LUSTIG.

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ATT O F? N EYS United States Patent Ofiice 2,711,093 Patented June 21,19 55 STOP MOTION Abraham Edelmau, New York, N. Y., Robert H.Roughsedge, Ramsey, N. J., and Hans G. Lustig, New York, N. Y.,assignors to Celanese Corporation of America, New York, N. Y., acorporation of Delaware Appiication June 25, 1949, Serial No. 101,405

15 Claims; (Cl. 66-163) This invention relates to stop motions, andrelates more particularly to photoelectric stop motions for warpknitting machines.

In textile machines wherein yarn is handled in the form of a warp, it isdesirable to provide a stop motion which will give a warning or stopsuch machines upon breakage of a warp yarn, whereby the production offabrics or other textile materials containing defects is substantiallyprevented. Mechanical stop motions, in which a drop wire is provided toride on each of the warp yarns, have come into widespread use withcertain types of textile machines, such as looms, having a relativelysmall number of yarns in each warp. However, mechanical stop motions arenot suited for other types of textile machines, such as warp knittingmachines having several thousand yarns in each warp, because of the lackof sufficient space for the requisite number of drop wires and becauseof the additional expense involved in positioning said drop wires whenstarting the machine.

It has previously been proposed to equip textile machines, such as warpknitting machines, with photoelectric stop motions which would givewarning or stop the machine when a broken yarn passed through a beam oflight impinging upon a phototube connected to a suitable amplifier.However, these photoelectric stop motions have not been satisfactory andhave, therefore, not come into commercial use. When these photoelectricstop motions were made sufficiently sensitive to respond to the passageof a single yarn having a diameter of the order of 0.004 inch, or less,through the light beam, they would often respond to spurious signalswhen none of the yarns was broken. For example, electrical surgesproduced by the starting and stopping of other machines, line voltagefluctuations, mechanical shocks and vibration, and particles of dust andlint would cause the photoelectric stop motions to operate. In

addition, frequent readjustment of the photoelectric stop motions wasrequired to compensate for the ageing of the light source and the tubesin the amplifier, which ageing reduced the intensity of the light beamand altered the effective sensitivity of the amplifying circuit. On theother hand, if the sensitivity of the photoelectric stop motions werereduced so that they would no longer respond to spurious signals, theywould often fail to operate when a yarn did break. When this occurred,defective fabrics or other textile materials would be produced.

Because no satisfactory stop motions were available for certain types oftextile machines, such as warp knitting machines, it has heretofore beennecessary to supervise these machines constantly during operation todetect and correct yarn breaks as they occurred. As will be readilyapparent, this greatly increases the cost of the fabrics or othermaterials produced by said textile machines.

It is an important object of this invention to provide a stop motionwhich will be free from the foregoing and other disadvantages of theprior stop motions, and which will be especially efiicient in operationand simple in construction.

A further object of this invention is the provision of a photoelectricstop motion, which will not respond to spurious signals and will notrequire frequent readjustment, but which will operate consistently uponbreakage of a yarn to give a warning or stop the textile machine towhich it is connected.

Other objects of this invention, together with certain details ofconstruction and combinations of parts, will be apparent from thefollowing detailed description and claims.

In accordance with this invention, there is provided a photoelectricstop motion, comprising two beams of light, two phototubes upon whichthe beams of light impinge and an amplifier which is responsive to thedifference in the signal from the phototubes caused by the variation inthe intensity of the light beams when a yarn passes through one of thelight beams. In certain textile machines, wherein two warps of yarn arehandled, such as two-bar warp knitting machines, one light beam ispositioned to pass adjacent to each of the warps. In other textilemachines, wherein only a single warp is handled, one light beam ispositioned to pass adjacent to said warp, and the other light beam ispositioned to pass through a path of equal length at a point spaced fromthe first light beam. The second light beam may be positioned adjacentthe first light beam so that a broken yarn will pass through both lightbeams in succession. Alternatively, the second light beam may bepositioned at a point completely removed from the warp.

Each of the two light beams may originate in a light projectorcomprising a lamp housing having a lamp mounted therein and providedwith a lens to focus the light from said lamp into a beam. It ispreferred to employ a widely diverging light beam, so that shifts in therelative position of the light projector and phototube will cause aminimum of variation in the efiective intensity of the light impingingon the phototube. The lamp housing is supported by shock-absorbingmounts, which are designed particularly to minimize the transmission ofhigh-frequency mechanical shocks and vibration to the lamp so that atmost the lamp will be subjected to low-frequency shocks and vibration.To produce the light beam, it is preferred to employ a lamp of theincandescent type having a heavy tungsten filament possessing a highthermal inertia, such as an automobile headlight lamp so that the lightoutput of the lamp cannot change at a rapid rate with variations in lampvoltage. To assist further in maintaining the light output constant, thelamp is energized by direct current which is filtered to remove anycyclic variations therefrom. Instead of providing a separate lightprojector and lamp for each light beam, the two light beams may bederived from a single lamp through suitable optical means.

The light projectors are positioned at one side of the warp and delivera beam of light in the general direction of light receivers, which arepositioned at the other side of the warp. The light receivers eachcomprise a housing having a phototube and a preamplifier tube mountedtherein. Like the lamp housing, the light receiver housing is supportedby shock-absorbing mounts to minimize the transmission of mechanicalshocks and vibration to the phototube and preamplifier tube.

The output signals from the preamplifier tubesare fed into a comparisoncircuit, wherein electrical surges, line voltage fluctuations and theresidue of cyclic variations in the lamp current are balanced out sincethey affect both phototubes and both lamps in the same way, causing thelight output of the lamps to vary simultaneously. Thus,

each light beam acts as a referencefor the other and so long as both arefluctuating in the same manner there will be no difference between them.The circuit in which the output signals of the preamplifier tubes arecompared is designed so that it always tends toward equilibrium or zerooutput. As a result, this circuit automatically compensates for anypermanentor semi-permanent differences in the output signals from thepreamplifier tubes which may be caused by differences in the lightoutput of the lamps or the sensitivity of the phototubes andpreamplifier tubes. It is, therefore, unnecessary to employ preciselymatched lamps, or preamplifier tubes or to make adjustmentsto'compensate for the unequal variations of the components due to anycause, such as age, for example.

To insure that any broken yarn in a warp does not become entangledwithand is not carried along by the remaining yarns in the warp, means areprovided to force the broken yarn through the light beam. This means maytake the form of a conduitpositioned adjacent the warp and provided witha series of apertures through which a stream of air is directed at thewarp. The velocity of the :stream of air regulates the speed at whichthe broken yarn -moves, controlling the time required for the yarn topass through the light beam and the length of the signal producedthereby.

The signal resulting when a yarn passes through one of the light beamsis differentiated in the comparison cir- I cuit creating a negative anda positive pulse. lln'this way, the passage of a yarn through eitherlight beam is made to create pulses of both polarities which can behandled alike. The pulses are filtered to eliminate therefrom extremelyslow and extremely rapid variations which can- 1 ,not represent a brokenyarn.

The filtering circuits are designed so as to eliminate any pulses thatresult from the low-frequency shocks and vibration that may pass to thelamp through the shock mounts supporting the light projector. The pulsesare also compared with a reference voltage. If the pulse is larger thanthis voltage, it passes through the circuit. Otherwise it is completelysup- ..pressed. The sensitivity of the stop motion may be adjustedreadily-by altering the value of this reference voltage. The pulse isthen lengthened and amplified in a power amplifier, and the current fromsaid amplifier is employed to give a warning or to cause the textilemachine to which the stop motion is connected to stop. When the brokenyarn has been repaired, the textile machine may be put back intooperation without the neces-i sityfor resetting thephotoelectricstop-motion in any way.

The photoelectric stop motion of this invention produces the bestresults when two beams of light and two phototubes are employed therein.However, satisfactory results may also be obtained by using a singlebeam of light and a single phototube and passing the signal from thisphototube through the amplifier described herein.

Whilethe fluctuations produced by electricalsurges, line voltagefluctuations and the residue of any cyclic variations in lamp currentwill not be balanced out with a single phototube, the tendency of thecircuit toward equilibrium or Zero output, the filtering and thesensitivity adjustment will eliminate most of these spurious signals andprevent the operation of the photoelectric stop motion in responsethereto.

A preferred embodiment of our photoelectric stop motion applied to atwo-bar warp knitting machine will now be described in connection withthe accompanying drawings in which Fig. l is a side elevational view ofthe warp knitting machine showing the devices of this invention appliedthereto,

.Fig. 2 is a view, partly in section, showing the light projector andlight receiver arrangement,

Fig. 3 is a circuit diagram of theamplifier circuit,and

Fig. 4 is a circuit diagram of the power supply for the amplifier inFig. 3.

Like reference numerals indicate like parts throughout the several viewsof the drawings.

Referring now to the drawings, the reference numeral 11 designates theframe members of a two-bar warp knitting machine on which are supportedwarp beams 12 and 13 and tension rods 14 and '15 over which warps 16 and17 are passed on their way to knitting elements indicated generally byreference numeral 18. These knitting elements, as is well understood inthe art, are operated from the cam shaft 19 and knit the warps 16 and 17into a fabric 21, which passes over guide rod 22, under roller 23 and onto take-up roller 24.

Positioned above the warps 16 and 17 is a conduit 25 having a pluralityof apertures 26 therein, from which a stream of air under pressure isdirected onto the warps to force any broken yarns downwardly. The airpressure in the conduit 25 is regulated so that the yarns fall at a rateof between about 5 and inches per second, which produces a pulse ofbetween about 0.1 and 0.005 second when the yarn passes through a lightbeam having an efiective diameter of about 0.5 inch.

Light projectors 27 supported by shock-mounts 28 -fastened to the framemember 11 are positioned to one side of the warps 16 and 17. .Each lightprojector 27 comprises a housing 29, an incandescent lamp 30 mountedtherein, a tube 31 extending from said housing and a lens 32 positionedin said tube and acting to focus the light from the lamp 30 into a beamwhich passes under the warp 16 or 17. After traversing the warp, thebeam of light from the light projector 27 is picked up by a lightreceiver 33 supported by shock-mounts 34 fastened to the frame member11. The light receiver 33 comprisesa light-proof housing 35, a phototube36 supported therein on shock-mounts 37, a light admitting tube 38extending from said housing and a preamplifier tube 39, which amplifiesthe signalfrom the phototube 36. A mask .41 having an aperture 42therein is positioned in the light admitting tube 38 to limit theeffective diameter of the portion of the light beam viewed by thephototube 36. An optical system may be provided in the light receiver 33to focus the light beam onto the phototube 36. However, a suflicientlystrong signal may be obtained without such opticalsystem for mostapplications.

Referring now to Figs. 3 and 4 of the drawings Where in the circuit ofthe photoelectric stop motion is shown, the phototubes 36 have theiranodes connected to the plates-and their cathodes connected tothecontrol grids of preamplifier tubes 39. The cathodes of thepreamplifier tubes 39 are connected to ground through resistors 43 and44 and potentiometer 45, and the control grids of said preamplifiertubes are connected to ground through resistors 46. With theseconnections, the cathodes of the preamplifier tubes 39 follow thepotential variations of the control grids, and the change in relativepotential between the cathodes and the control grids is 7 small, evenwhen signals of considerable magnitude occur.

The phototubes 36 and preamplifier tubes 39 are shielded from magneticand electric fields by magnetic shields 47 and electrostatic shields 48.These shields may be combined by using a conductive iron or steelhousing, but at some sacrifice'in shielding efiiciency. In addition,each phototube 36 is enclosed in an inner optical and electrical shield49, which is insulatedfrom ground and connected to the cathode of thepreamplifier tube 39. Since the potential variations of the cathode ofthe preamplifier tube 39, to which the shield 49 is connected, followthe potential variations of the control grid of said preamplifier tube,the potential dilfere'nce on the capacitor formed between the phototube36 and its wiring, on one side, and the shield 49, on the other side,remains substantially constant. As a result, no large charging currentfor this capacitor need flow to the phototube 36 through the gridcircuit wiring of the preamplifier tube 39. -If the inner shield 49 wereomitted,

as is usually done, or if the inner shield weregrounded,

the changes in the grid potential of the preamplifier tube 39 due to asignal from the phototube 36 would require that the capacitor formedbetween the phototube 36 and its surroundings be charged or dischargedto match the grid potential. This would force a charging current to flowthrough the grid circuit wires of the preamplifier tube 39 and influencethe grid of said tube adversely. The effect of this charging currentwould be to prevent quick response of the preamplifier tube 39 tosignals from the phototube 36, reducing the overall sensitivity of theamplifier.

During operation, a positive voltage is applied to the anodes of thephototubes 36 and the plates of the preamplifier tubes 39 from theterminal 51 through the dropping resistor 52. This voltage is dividedbetween the resistor 46 and the phototube 36 in accordance with theintensity of the light striking the phototube at each instant. When ayarn enters the beam of light striking one of the phototubes 36, thelight to the phototube decreases, the current through the phototubediminishes and the voltage across the resistor 46 drops, since thisvoltage is due solely to the current flowing through the phototube. Thedrop in the voltage across the resistor 46 swings the grid of thepreamplifier tube 39 connected thereto negatively, causing the cathodeof said preamplifier tube to swing negatively by the same amount. Inlike manner, the cathode of the preamplifier tube 39 swings positivelywhen the yarn leaves the beam of light striking one of the phototubes36.

The cathode potentials of the preamplifier tubes 39 are compared in aseries circuit comprising a capacitor 53 and primary winding 54 of atransformer 55 having a secondary winding 56, which circuit is connectedat one end between the resistors 43 and 44 and at the other end to thetap on the potentiometer 45. By adjusting the potentiometer 45, whichacts as a balance control, it is possible to equalize the efiects ofline voltage fluctuations, electrical surges, vibration, etc. A perfectadjustment of the potentiometer 45 is not necessary, since any permanentunbalance simply results in a steady voltage across the capacitor 53,and does not cause a current to flow through said capacitor and theprimary winding 54. However, when a yarn enters the beam of lightstriking one of the phototubes 36 and causes the cathode of thepreamplifier tube 39 connected to said phototube to capacitor 53 and theprimary winding 54 in one direction until the voltage across saidcapacitor has been changed by an amount equal to the change in cathodepotential.

.Similarly, when the yarn leaves the light beam causing the cathode ofthe preamplifier tubes 39 to swing positively, a signal current flowsthrough the capacitor 53 and the primary winding 54 in the otherdirection until the voltage across said capacitor has again been changedby an amount equal to the change in cathode potential. The capacitor 53thus acts to differentiate any change in the cathode potential of thepreamplifier tubes 39, so

that the passage of a yarn through either of the light beams produces asignal current in both directions through the primary winding 54. Asimilar differentiating effect may be obtained from the transformer 55.As a result, the amplifier need be responsive to a signal of only onetype. The magnitude of the current flowing through the primary winding54 depends upon the rate of change of the difference in potentialbetween the .swing negatively, a signal current flows through the thelight beam passes through the transformer 55 to the control grid of anamplifier tube 57, which is biased negative almost to cut oil. Becauseof the high negative bias on the control grid of the amplifier tube 57,negative polarity signals have little effect on the plate current ofsaid tube, but positive polarity signals cause a marked increase inplate current. This increase in plate current causes a negative signalto be applied to the control grid of an amplifier tube 53, which isbiased slightly negative so that maximum plate current flows through itnormally with no signal. Because of the slight negative bias on controlgrid of the amplifier tube 58, positive polarity signals have littleeifect on the plate current of said tube, but negative polarity signalscause a marked decrease in plate current. The polarity and biasingarrangements of the amplifier tubes 57 and 58 make the amplifierselectively responsive to signals of one polarity and greatly decreasethe responsiveness of the amplifier to signals of diflerent polarity.Any signals that vary more rapidly than a predetermined maximum,representing the passage of a yarn through the light beam at the highestspeed, are bypassed to ground by capacitors 59, 61 and 62, which areconnected to the plates of the preamplifier tubes 39 and the amplifiertubes 57 and 58, respectively. As a result, these rapidly varyingsignals have only a slight effect on the plate current of the amplifiertube 58 and do not cause operation of the photoelectric stop motion, aswill be described more fully hereinafter.

The decrease in the plate current of the amplifier tube 58 produced bythe passage of a yarn through the light beam causes a positive signal tobe applied to the control grid of a clipper tube 63, which is biasedbeyond the cutoff point so that no current normally flows through itsplate circuit. When the amplitude of the positive signal applied to thecontrol grid of clipper tube 63 is sufiiciently great, a current flowsmomentarily through the plate circuit of said tube. However, when theamplitude of the positive signal applied to the control grid of theclipper tube 63 is less than a predetermined minimum, such as resultsfrom extremely slow or extremely rapid variations in light intensity, nocurrent flows in the plate circuit of said tube. The amplitude of thepositive signal necessary to cause a current to flow in the platecircuit of the clipper tube 63 depends upon the bias voltage applied tosaid tube and may be controlled by means of a variable resistor 64,which acts as a sensitivity control.

The momentary flow of current in the plate circuit of the clipper-tube63 causes a large increase in the charge on a capacitor 65 which isconnected in series with said plate. After the fiow of current in theplate circuit of the clipper tube 63 ceases, the capacitor 65 dischargesslowly through a resistor 66, connected across its terminals, whoseresistance is selected so that it takes approximately 0.30.4 second forthe capacitor to discharge, During the interval of time for which thecapacitor 65 has a charge thereon, there is a negative signal applied tothe control grid of an amplifier tube 67, and this causes acorresponding positive signal to be applied to the control grid of apower amplifier tube 68 causing current to flow in the plate circuit ofsaid tube, which circuit includes a relay coil 69 shunted by a capacitor71. The flow of current through the relay coil 69 operates the contacts72 to stop the textile machine to which the stop motion is connected orto give a warning that yarn breakage has occurred.

The power supply for the amplifier includes an alternating current powerline 73, which is connected to the primary winding 74 of a transformer75 having secondary windings 76, 77, 78 and 79. The secondary winding 76is connected to a bridge rectifier 81, which furnishes current toterminals 82 through a variable resistor 83 and a filter, comprisingcapacitors 84 and 85 and a choke coil 86. From the terminals 82,filtered direct current is supplied to the lamps 39 through terminals87, and also to the filaments of the preamplifier tubes 39 throughterminals 88. Filtered direct current is used on the filaments of thepreamplifier tubes 39 to minimize the ripple which would otherwise beintroduced into the amplifier. The filaments of all the other vacuumtubes in the amplifier are supplied with alternating current from thesecondary winding 77. The high voltage supply for the amplifier isobtained from the secondary winding 78, which is connected to afull-wave rectifier 89 whose filament is energized from the secondarywinding 79. After being rectified, the high voltage is filtered by meansof capacitors 91 and 92 and choke coil 93. The filtered, high-voltage isconnected to terminals 94, and 96 through dropping resistors 98, 99 and101. The terminal 94 supplies current to the terminal 51 for thephototubes 36, the preamplifier tubes 39 and the amplifier tubes 57 and58. The terminal 95 supplies current to a terminal 162 for the clippertube 63 and amplifier tube 67, and the terminal 96 supplies current to aterminal 103 for the power amplifier tube 68. Voltage stabilizing tubes104, 105 and 106 are connected across the high voltage supply to assistin maintaining a constant voltage on the amplifier.

While the photoelectric stop motion of this invention is especiallyuseful with warp knitting machines, it is also applicable to other typesof textile machines and to various other equipments wherein it isdesired to employ variations in the intensity of a light beam forcontrol purposes.

It is to be understood that the foregoing detailed description is givenmerely by way of illustration and that many variations may be madetherein without departing from the spirit of our invention.

Having described our invention, what we desire to secure by LettersPatent is:

l. A photoelectric stop motion, comprising a phototube, means forprojecting a beam of light onto said phototube, operatively connected tothe phototube an amplifier including means for comparing the signal fromthe phototube with a reference voltage whereby signals below apredetermined value will not cause operation of the stop motion, andmeans connected to the amplifier for stopping the operation of a machinewhen the signals exceed said predetermined value.

2. A photoelectric stop motion, comprising a pair of phototubes, meansfor projecting a beam of light onto each of said phototubes, operativelyconnected to the phototubes an amplifier responsive to the difierence inthe signal from the phototubes when the illumination on one of thephototubes is varied including means for comparing the difierence insignals from the phototubes with a reference voltage whereby adifference in signals below a predetermined value will not causeoperation of the stop motion, and means connected to the amplifier forstopping the operation of a machine when the signals exceed saidpredetermined value.

3. A photoelectric stop motion, comprising a phototube, means forprojecting a beam of light onto said phototube, and operativelyconnected to the phototube an amplifier including means fordifferentiating the signal from the phototube whereby both a negativeand a positive pulse are produced when the illumination on the phototubeis varied, and means for amplifying pulses of one polarity only.

4. A photoelectric stop motion, comprising a pair of phototubes, meansfor projecting a beam of light into each of said phototubes, andoperatively connected to the phototubes an amplifier responsive to thedifference in the signal from the phototubes when the illumination onone of the phototubes is varied, including means for difierentiating thedifference in signals from the phototubes whereby both a negative and apositive pulse are produced when the illumination on one of thephototubes is varied, and means for amplifying pulses of one polarityonly.

5. A photoelectric stop motion, comprising a pair of phototubes, meansfor simultaneously projecting beams of light of substantially equalintensity onto said phototubes whereby the phototubes will normally emitsignals of equal intensity, and, operatively connected .to the phototubes, an amplifier responsive to the ditference in: the signal from thephototubes when the illumination on one of the phototubes is varied,whereby said amplifier will pass a signal when the illumination on oneonly of'the phototubes is varied, said amplifier including filteringmeans for eliminating signals having a frequency outside a predeterminedrange. I g

6. A photoelectric stop motion for a textile machine wherein a warp ofyarns is handled, comprising a phototube positioned at one side of saidwarp, means positioned at the other side of the warp for projecting abeam 'of light onto the phototube, a second phototube, means forprojecting a beam of light onto said second phototube, and operativelyconnected to the phototubes means responsive to the difference insignals from the phototubes when a warp yarn passes through the lightbeam.

7. A photoelectric stop motion for a textile machine wherein a warp ofyarns is handled, comprising a photo tube positioned at one side of thewarp, means positioned at the other side of the warp for projecting abeamof light onto the phototube, a second phototube, means forprojecting a beam of light having a path equal in length to the lengthof the first beam of light onto said second phototube, and operativelyconnected to the phototubes an amplifier responsive to the differenceinthe signals from the phototubes when a warp yarn passes through thelight beam.

8. A photoelectric stop motion for a textile machine wherein a warp ofyarns is handled, comprising a phototube positioned at one side of thewarp, means positioned at the other side of the warp for projecting abeam of A light onto the phototube, means for forcing a broken yarnthrough the light beam, a second phototube, means for projecting a beamof light having a path equal in length to the length of the first beamof light onto said second phototube, and operatively connected to thephototubes an amplifier responsive to the difierence in the signals fromthe phototubes when a warp yarn passes through the light beam.

9. A photoelectric stop motion for a two-bar warp knitting machinewherein two warps of yarn are knitted into a fabric, comprising aphototube positioned atone side of each of the warps, means positionedat the other side of each of the warps for projecting a beam of lightonto each of the phototubes, and operatively connected to the phototubesan amplifier responsive to the difierence in the signals from thephototubes when a warp yarn passes through either light beam.

10. A photoelectric stop motion for a two-bar warp knitting machinewherein two warps of yarn are knitted into a fabric, comprising aphototube positioned at one side of each of the warps, means positionedat the other side of each of the warps for projecting a beam of lightonto each of the phototubes, and operatively connected to the phototubesan amplifier responsive to the difference passes through either lightbeam including a circuit in which the signals from the phototubes arecompared;

11. A photoelectric stop motion for a two-bar warp knitting machinewherein two warps of yarn are knitted into a fabric, comprising aphototube positioned at one side of each of the warps, means positionedat the other side of each of the warps for projecting a beam. of lightonto each of the phototubes, and operatively connected to the phototubesan amplifier responsive to the difference in the signals from thephototubes when a warp yarn passes through either light beam including acircuit containing a series condenser in which the signals from thephototubes are compared whereby both a negative and a positive pulse areproduced when a yarn passes through knitting machine wherein two warpsof yarn are knitted into a fabric, comprising a phototube positioned atone side of each of the warps, means positioned at the other side ofeach of the warps for projecting a beam of light onto each of thephototubes, and operatively connected to the phototubes an amplifierresponsive to the difference in the signals from the phototubes when awarp yarn passes through either light beam including a circuitcontaining a series condenser in which the signals from the photoubesare compared whereby both a negative and a positive pulse are producedwhen a yarn passes through a light beam, and means including anamplifier tube having a high negative bias and an amplifier tube havinga slight negative bias connected in series for selectively amplifyingthe positive pulse.

13. A photoelectric stop motion for a two-bar warp knitting machinewherein two warps of yarn are knitted into a fabric, comprising aphototube positioned at one side of each of the warps, means positionedat the other side of each of the warps for projecting a beam of lightonto each of the phototubes, means positioned adjacent each of the warpsfor forcing a broken yarn through the light beam, and operativelyconnected to the phototubes an amplifier responsive to the diiference inthe signals from the phototubes when a warp yarn passes through eitherlight beam including a circuit containing a series condenser in whichthe signals from the phototubes are compared whereby both a negative anda positive pulse are produced when a yarn passes through a light beam,and means including an amplifier tube having a high negative bias and anamplifier tube having a slight negative bias connected in series forselectively amplifying the positive pulse.

14. A photoelectric stop motion for a two bar warp knitting machinewherein two warps of yarn are knitted into a fabric, comprising aphototube positioned at one side of each of the warps, means positionedat the other side of each of the warps for projecting a beam of lightonto each of the phototubes, means positioned adjacent each of the warpsfor forcing a broken yarn through the light beam, and operativelyconnected to the phototubes an amplifier responsive to the difference inthe signals from the phototubes when a warp yarn passes through eitherlight beam including a circuit containing a series condenser in whichthe signals from the phototubes are compared whereby both a negative anda positive pulse are produced when a yarn passes through a light beam,means including an amplifier tube having a high negative bias and anamplifier tube having a slight negative bias connected in series forselectively amplifying the positive pulse, means for lengthening saidpositive pulse, and filtering means for eliminating undesired signals.

15. A photoelectric stop motion, comprising a phototube, means forprojecting a beam of light onto said phototube, mounts for said lightprojector including means for minimizing the transmission ofhigh-frequency mechanical shocks and vibration thereto whereby the lightprojector will be subjected at most to low-frequency shocks andvibration, and operatively connected to the phototube an amplifierincluding filtering means for eliminating the signals produced by saidlow-frequency shocks and vibration.

References Cited in the file of this patent UNITED STATES PATENTS1,919,888 Hough July 25, 1933 2,078,762 Holst Apr. 27, 1937 2,139,474Shepard Dec. 6, 1938 2,208,447 Berry July 6, 1940 2,233,483 Metcalf Mar.4, 1941 2,281,621 Rust et al. May 5, 1942 2,320,977 Nicolson June 1,1943 2,438,365 Hepp Mar. 23, 1948 2,442,240 Hooker et al May 25, 19482,495,511 Dolberg Jan. 24, 1950 2,522,101 Dion et a1 Sept. 12, 19502,556,692 Holdaway June 12, 1951

14. A PHOTOELECTRIC STOP MOTION FOR A TWO BAR WARP KNITTING MACHINEWHEREIN TWO WRAPS OF YARN ARE KNITTED INTO A FABRIC, COMPRISING APHOTOELECTRIC POSITIONED AT OBNE SIDE OF EACH OF THE WRAPS, MEANSPOSITIONED AT THE OTHER SIDE OF EACH OF THE WRAPS FOR PROJECTING A BEAMOF LIGHT INTO EACH OF THE PHOTOTUBES, MEANS POSITIONED ADJACENT EACH OFTHE WRAPS FOR FORCING A BROKEN YARN THROUGH THE LIGHT BEAM, ANDOPERATIVELY CONNECTED TO THE PHOTOTUBES AN AMPLIFER RESPONSIVE TO THEDIFFERENCE IN THE SIGNALS FROM THE PHOTOTUBES WHEN A WRAP YARN PASSESTHROUGH EITHER LIGHT BEAM INCLUDING A CIRCUIT CONTAINING A SERIESCONDENSER IN WHICH THE SIGNALS FROM THE PHOTOTUBES ARE COMPARED WHEREBYBOTH A NEGATIVE AND A POSITIVE PLUSE ARE PRODUCED WHEN A YARN PASSESTHROUGH A LIGHT BEAM, MEANS INCLUDING AN AMPLIFIER TUBE HAVING A HIGHNEGATIVE BIAS AND AN AMPLIFIER TUBE HAVING A SLIGHT NEGATIVE BIASCONNECTED IN SERIES FOR SELECTIVELY AMPLIFYING THE POSITIVE PLUSE, MEANSFOR LENGTHENING SAID POSITIVE PLUS, AND FILTERING MEANS FOR ELIMINATINGUNDERSIRED SIGNALS.